The inventors earlier reported that a charge-transporting thin-film obtained from an organic solvent-based charge-transporting varnish which contains a charge-transporting material composed of a low-molecular-weight oligoaniline compound exhibits excellent electroluminescent device characteristics (see Patent Document 1).
In the charge-transporting varnish of Patent Document 1, the low-molecular-weight oligoaniline compound making up the charge-transporting material possesses within the molecule an identical repeating unit structure and has the property of becoming increasingly colored with extension of the conjugated system such that, when the varnish is rendered into a charge-transporting thin-film, light absorption in the visible wavelength spectrum increases.
Coloration of the charge-transporting thin-film is known to decrease the color purity and color reproducibility of an organic electroluminescent (abbreviated below as “organic EL”) device.
Moreover, such coloration is a problem in various full-color technologies used in organic EL displays, such as tri-color emission, the color-by-white approach and color-changing methods, becoming a major obstacle to the stable production of organic EL devices.
Hence, there exists a desire for charge-transporting thin-films in organic EL devices to have a high transmittance in the visible wavelength spectrum and a high transparency.
In light of this, the inventors earlier found that a charge-transporting thin-film with suppressed coloration in the visible spectrum and excellent transparency can be obtained by using an oligoaniline compound wherein a portion of the conjugated system within the molecule has been cut or an oligoaniline compound which includes in some portion thereof a conjugated system composed of a structure of repeating units differing from aniline units (see Patent Document 2). However, a thin-film having an even higher transparency is now desired in order to enhance, for example, the light-extracting efficiency. Moreover, in organic EL devices which include the thin-film of Patent Document 2, there remains room for improvement in, for example, the device characteristics and lifespan.